Phenolic resin compositions

ABSTRACT

Phenolic resin compositions. 
     Phenolic resin compositions containing an additive consisting of at least 20% by weight of an alkaline or alkaline-earth metaborate relative to the total weight of the additive. 
     Applications to the manufacture of phenolic pre-preg mats which are stable in storage.

This is a continuation of application Ser. No. 07/118,063, filed Nov. 6,1987, now U.S. Pat. No. 4,912,178 which is a cont. of Ser. No.06/762,482, filed Aug. 5, 1985, now abandoned.

The present invention relates to new phenolic resin compositions; itssubject is more particularly phenolic resin compositions which areparticularly suitable for the manufacture of "phenolic prepreg mats".

Prepregs are mixed materials which are prepared from thermosettingresins and reinforcements and, if appropriate, fillers. Thereinforcement employed is in the form of fibres such as cellulosicfibres or glass fibres, in particular glass fibre rovings, of nonwovenfabric, for example made of a high molecular weight polyester or ofpolyvinyl chloride, of glass fibre mat or cloth made, for example of anaromatic polyamide, glass or asbestos. These prepreg materials have theadvantage of being capable of being directly moulded in the presswithout the need to prepare beforehand a mixture consisting of resin,catalysts, fillers and pigments . Prepregs can be divided into twoclasses: on the one hand, "non-flowable" prepregs and, on the otherhand, "flowable" prepregs. "Nonflowable" prepregs generally consist onlyof glass fibre reinforcements impregnated with a suitable resin taken toan appropriate partial polymerization stage, known as "B-stage". At thisstage, the resins are practically tack-free but are still soluble andfusible. When placed in a heated press, such a mixed material permits amovement of the resin between the fibres and results in a uniformdistribution of glass and resin. After the mould has been closed, theresin is fully hardened Non-flowable prepregs are manufactured fromepoxy resins, phenol-formaldehyde resins and also polyester resins basedon diallyl phthalate. Such materials permit particularly restrictedapplications because in most cases they have the disadvantage ofdisintegrating when used; they are used, for example, for themanufacture of printed circuits.

Known "flowable" prepregs which are called "prepreg mats" in most caseshave hitherto been prepared only from a single class of resins, namelypolyester resins. Depending on the manufacturing method employed, twovarieties of "prepreg mats" can be characterised in particular.

SMC (sheet moulding compound) prepregs are mixed materials consisting ofa sheet of chopped glass filaments which is preimpregnated with afilled, pigmented and catalysed resin. They are introduced between twolayer-forming films (for example polyethylene), which facilitateshandling. They are then used in compression moulding.

Bulk moulding compounds (BMC) are mixtures consisting of a thermosettingresin, filler and chopped glass filaments; it comes in bulk or inextruded form, ready for use.

After heat-maturing, the prepreg mat produced in this way has aconsistency which is similar to that of leather or of an oilcloth. Afterstorage in a maturation chamber the prepreg mat thus produced can bestored for approximately three months, a period during which it can beemployed for moulding using heat and under pressure.

The major difficulty which needs to be overcome in order to manufacturethese prepreg mats based on polyester resins is to have available aresin which is sufficiently fluid to be capable of impregnating thechopped glass filament matting, but the viscosity change of which duringthe first 48 hours (a period after which the viscosity should showvirtually no further variation at ambient temperature) should besufficiently fast to make it possible to produce a prepreg mat havingthe required consistency which should be close to that of leather orthat of an oil cloth, as indicated above. It can be seen, therefore,that in practice there are two mutually opposed problems to be solved.To solve such problems it is known to add to the polyester resin athickener chosen from alkaline-earth oxides, such as magnesium oxide.The addition of such a compound to the polyester resin makes it possibleto obtain a resin having a required viscosity but also an adequatestability which permits the resin not to increase too fast in viscosityat the risk of obtaining a poor impregnation of the chopped glassfilament matting.

It might have been thought that merely transferring the alkaline earthoxides employed for the polyester resins to the phenolic resins wouldhave made it possible to obtain phenolic resin dough compositionssuitable for the manufacture of phenolic prepreg mats. Unfortunatelythis is not the case at all. It is found, in fact, that the addition ofan alkaline-earth oxide to phenolic resins produces resin compositionswhich are not homogeneous, consisting, in particular, of a surface crustand crystals of alkaline-earth oxide in the composition. Furthermore,the use of an alkaline-earth oxide alone in the phenolic resins resultsin an exothermic reaction which can be responsible for a decompositionof the catalyst used for hardening. In addition, the use of analkaline-earth oxide results in formulations which require a prohibitivemoulding time (approximately 2 minutes per mm) owing to an inhibitioncaused by this oxide.

The present invention relates to new phenolic resin compositionssuitable for the manufacture of phenolic prepreg mats according to whichthe compositions employed for impregnating the fibre mats consist ofphenol-form-aldehyde resins of resolt-types, fillers, pigments andhardening agents, characterised in that these compositions contain anadditive consisting of at least 20 % by weight of an alkaline oralkaline-earth metaborate relative to the total weight of the additive.

According to the invention, the alkaline or alkaline-earth metaborate isused with an alkaline-earth oxide, this oxide being employed in aquantity which is at most equal to 80 % by weight relative to the totalweight of the additive.

It has been found, in fact, that the use of such an additive makes itpossible to obtain a homogeneous resin composition, a composition theviscosity of which changes during the first forty-eight hours, to becomestable thereafter. This produces a composition which is endowed withproperties such that it permits the manufacture of prepreg mats.

According to another characteristic of the compositions of theinvention, the quantity of additive used is equal to at most 60 % byweight relative to the weight of the phenolic resin solution used, andpreferably between 5 and 40 % by weight. Below 5 % virtually no effecton the viscosity of the composition is observed; above 60 % by weight itis no longer possible to control the viscosity of the composition, whichmakes it unsuitable for the manufacture of prepreg mats.

The compositions which are the subject of the invention consist of aphenolic resin and an additive consisting of at least 20 % by weight ofan alkaline-earth or alkaline metaborate, relative to the total weightof the additive.

According to the invention, the alkaline-earth or alkaline metaborate isused with an alkaline-earth oxide, this oxide being employed in aquantity which is at most equal to 80 % by weight relative to the totalweight of the additive. Depending on the characteristics of the phenolicresins used, the composition of the additive is adapted; it can containup to 100 % by weight of alkaline-earth or alkaline metaborate, butalways at least 20 % by weight of alkaline or alkaline-earth metaborate.

The alkaline or alkaline-earth metaborates employed to produce thephenolic resin compositions which are the subject of the invention arepreferably chosen from barium, lithium or calcium metaborates. Thebarium salt is preferably employed, for reasons of availability and easeof procurement.

Magnesium oxide is preferably chosen among the alkaline-earth oxidesemployed.

The resin compositions which are the subject of the invention areprepared by adding the additive to the phenolic resin. Preferably, forreasons of stability and ease of dispersion, the additive is added tothe catalyst solution, the mixture obtained being then added to thephenolic resin.

Hardening of the phenolic resins is carried out, in a known manner, withthe aid of catalyst solutions consisting of a solvent and an acid; acidswhich may be mentioned in particular are para-toluenesulphonic acid,ortho-toluenesulphonic acid, benzenesulphonic acid and xylenesulphonicacid. Organic solvents are understood to mean the compounds containingalcohol groups methanol, ethanol, propanol, isopropanol, and polyolssuch as glycerol, dipropylene glycol and triethylene glycol. Knownlatent catalysts are suitable more particularly for the manufacture ofthe compositions according to the invention. Latent catalysts areunderstood to mean catalysts which are practically inactive at lowtemperature, but which become catalytically active at an elevatedtemperature required for the polycondensation of the resin. As latentcatalysts mention can be made, for example, of solutions consisting ofan alkyl ester, a toluenesulphonic acid, an organic solvent and atoluenesulphonic acid or concentrated sulphuric acid. The quantities ofhardeners employed are those conventionally employed for hardeningresols; these quantities are between 5 and 50 %, and preferably between10 and 40 % by weight relative to the weight of the resol solution.

The resols employed for the manufacture of the compositions according tothe invention are known resols prepared by the condensation offormaldehyde with phenol in the presence of an alkaLine catalyst. Theyare characterised by a F/P molar ratio of between 1.2 and 2.5 andoptionally contain additives such as plasticizers, surfactants, andfillers such as silica, kaolin or aluminium hydroxide.

The phenolic resin compositions which are the subject of the inventionare particularly suitable for the manufacture of phenolic prepreg mats.For the manufacture of prepregs, use is made in a known manner ofreinforcements consisting of chopped glass fibre filaments, choppedglass filament rovings, polyamide cloths, cellulosic fibres or carbonfibres. The quantity of fibres employed is such that the finishedprepreg mat contains at most 70 % thereof by weight relative to thetotal weight of the finished material.

The phenolic resin compositions which are the subject of the inventionmake it possible to manufacture prepreg mats with very good flow, andthey also make it possible to obtain phenolic prepreg mats which can bestored for at least 2 months before moulding at ambient temperature.Compared to the known prepreg mats manufactured from unsaturatedpolyester resins, phenolic prepreg mats have the advantage of exhibitingbetter fire and combustion resistance, which extends their areas ofapplication. In addition, the finished material has a better thermalbehaviour.

The prepreg mats obtained from the resin compositions which are thesubject of the invention can be used after storage, in a known manner,by being subjected in presses, for example, to pressures of between 40and 140 bars for 20 to 80 seconds per millimetre thickness at atemperature of between 110° and 150° C.

The following examples illustrate the present invention. The viscositiesare determined at 20° C.

The examples refer to viscosity measurements:

with phenolic resins alone

with phenolic resins containing a hardening-catalyst conventionallyemployed for the use of these resins

with phenolic resins to which a hardening-catalyst, fillers and glassfibres have been added.

EXAMPLE 1

100 parts by weight of a phenolic resin which has the followingcharacteristics are employed.

F/P molar ratio=1.5

dry extract: 72 % (determined on 4 grams of product in an ovencontrolled at 140° C. for 3 hours)

a reactivity of 80° C. (determined in accordance with a method whichconsists in measuring the exothermic peak of a resin to which 10 % ofsulphuric acid and ethanol have been added).

viscosity at 25° C.: 0.5 Pa s

13.3 parts of barium metaborate of formula BaB₂ O₄.H₂ O are added tothis resin at ambient temperature. A fine, homogeneous composition isobtained which remains homogeneous after thickening After 10 minutes theviscosity of the composition is 15 Pa s.

After 30 minutes the viscosity 300 Pa s.

After one hour it is 1000 Pa s.

After 22 hours it stabilizes at 2000 Pa s.

EXAMPLE 2

100 parts of the resin of Example 1 and, respectively, 8.5 and 10.5parts of magnesium oxide, which is a known thickener for polyesterresins, are used. To the two mixtures obtained are added 26.67 parts ofa hardeningcatalyst consisting of a mixture of methanol andparatoluenesulphonic acid; this catalyst is produced from one mole ofmethanol and one mole of para-toluenesulphonic acid.

It is found at the outset that the dispersion is difficult to produceand a composition consisting of a surface crust is obtained.

With 8.5 parts the following results are obtained:

After 30 minutes the viscosity of the mixture is 2000 Pa s

After one hour it is 1000 Pa s

After 22 hours it is only 1100 Pa s

After 10 days it is 30,000 Pa s

With 10.5 parts of magnesium oxide the following results are obtained.After 30 minutes the viscosity is 270,000 Pa s.

After one hour it is no longer measurable.

EXAMPLE 3

Example 1 is repeated, but with the use of 13.3 parts of an additiveconsisting of various proportions of alkaline metaborate and magnesiumoxide. Table 1 below shows the viscosity of the mixture obtained aftervarious periods of time by using different proportions of bariummetaborate and magnesium oxide.

                                      TABLE 1                                     __________________________________________________________________________    Weight                                                                        proportions                                                                   barium                                                                        metaborate/                                                                            VISCOSITY (Pa s)                                                     magnesium   30   1    2   3                                                   oxide    T.sub.o                                                                          minutes                                                                            hour hours                                                                             hours                                                                             1 day                                                                              2 days                                     __________________________________________________________________________    35/65    1200                                                                             >500,000                                                          50/50    120                                                                              5,000                                                                              >500,000                                                     65/35    100                                                                              1,900                                                                              3,000                                                                              30,000  >300,000                                        80/20    20 80   150          7,000                                                                              8,000                                      __________________________________________________________________________

EXAMPLE 4

Example 1 is repeated with barium metaborate replaced by lithium andcalcium metaborate, but using 26.67 parts of the catalyst employed inExample 2.

Table 2 shows the results obtained.

                  TABLE 2                                                         ______________________________________                                                VISCOSITY (Pa s)                                                                     30       1     2     3      1                                  Additive                                                                              T.sub.o                                                                              minutes  hour  hours hours  day                                ______________________________________                                        Lithium  6      22        70   210  300     130                               meta-                                                                         borate                                                                        Calcium 50     540      1,040 5,000        5,020                              meta-                                                                         borate                                                                        ______________________________________                                    

EXAMPLE 5

100 parts of a phenolic resin having the following characteristics areused:

F/P molar ratio: 1.5. Dry extract: 80 %. Exothermic peak: 110° C.

130 parts of alumina hydrate as filler

A mixture is then added, prepared from 13.3 parts of barium metaborateand 26.67 parts of a catalyst consisting of a mixture of methanol andpara-toluenesulphonic acid produced from one mole of methanol and onemole of para-toluenesulphonic acid.

The initial viscosity is 13 Pa s. It then changes as follows:

After one day 100,000 Pa s

After 5 days 200,000 Pa s

After 10 days 200,000 Pa s

A prepreg is then prepared from this composition using 70 parts of thecomposition and 30 parts of chopped glass fibres.

The prepreg obtained has a weight of 3,300 g per m².

This product can be stored for 3 months at ambient temperature.

It is then moulded at a pressure of 100 bars at a temperature of 145° C.for 90 seconds. A product which has a thickness of 3 mm is obtainedafter moulding.

It has the following characteristics:

Flexural modulus: 9,000 N/mm2 (French Standard NFT 51001)

Flexural strength: 1800 N/mm2 (French Standard NFT 51001)

Oxygen index: 90 % (French Standard NFT 51071)

Epiradiator: class M1 (French Standard NFP 92501).

EXAMPLE 6

Example 2 is repeated but with magnesium oxide replaced by 6.9 parts ofbarium metaborate and with the use of the same quantity of the samecatalyst.

The viscosity changes in the following manner:

Initial viscosity: 1.6 Pa s

Viscosity after 30 minutes: 11 Pa s

After 60 minutes: 11 Pa s

After 40 hours: 20 Pa s

EXAMPLE 7

Example 2 is repeated using 20 parts of barium metaborate. The viscosityvalues are as follows:

Initial viscosity 15 Pa s

Viscosity after 10 minutes: 15,000 Pa s

Viscosity after 20 minutes: 60,000 Pa s

Viscosity after 30 minutes greater than 200,000 Pa s

EXAMPLE 8

Example 6 is repeated using a resin which has a molar ratio F/P=1.2, aviscosity of 0.5 Pa s and a reactivity of 80° C.

To this resin are added 40 parts of a mixture consisting of 100 parts ofa catalyst employed in Example 2 and 40 parts of barium metaborate. Theviscosity changes in the following manner

Initial viscosity: 20 Pa s

Viscosity after 1 day: 4,000 Pa s

Viscosity after 4 days: 6,500 Pa s

Viscosity after 6 days: 8,000 Pa s

EXAMPLE 9

Example 8 is repeated but using a resin which has the followingcharacteristics:

Molar ratio F/P =2.5, a viscosity of 0.5 Pa s and a reactivity of 80° C.

The change in viscosity is as follows:

Initial viscosity: 28 Pa s

Viscosity after 1 day: 48,000 Pa s

Viscosity after 4 days: 5,000 Pa s

Viscosity after 6 days 10,000 Pa s

What is claimed is:
 1. A prepeg mat comprising a fiber mat impregnatedwith a phenol-formaldehyde resole resin having a formaldehyde-to-phenolratio of 1.2-2.5 and based on the resole resin from 5 to 60% by weightof an additive containing at least 20% by weight of a lithium metaborateor an alkaline earth metal borate.
 2. A prepeg mat according to claim 1,wherein the metaborate is present in combination with an alkaline-earthmetal oxide, the concentration of the oxide being not more than 80% byweight of the total of metaborate and oxide.
 3. A prepeg mat accordingto claim 1, wherein said metaborate being present in a quantity ofbetween 5 and 40% by weight relative to the weight of the resol resin.4. A prepeg mat according to claim 1, wherein the additive contains atleast 20% by weight of barium metaborate.
 5. A prepeg mat according toclaim 2, wherein the alkaline-earth metal oxide is magnesium oxide.